1. Field of the Invention
The invention relates to a snap gauge for checking dimensions of workpieces having a cylindrical surface, comprising: support means; reference means, substantially of Vee type, coupled to the support means for cooperating with the cylindrical surface of the workpiece; and measuring means including two movable arms arranged substantially along a longitudinal direction, two feelers coupled respectively to the ends of the movable arms for contacting the workpiece, and transducer means associated with the movable arms for providing a signal depending on the mutual distance between the feelers.
2. Description of the Prior Art
A manual electronic snap gauge, which is known from Italian patent application No. 3525A/81 of Sept. 14, 1981, comprises a substantially U-shaped metal support frame carrying a support plate supporting one or more pairs of gauging heads, arranged between the legs of the frame. A Vee reference element is fixed to the support plate for cooperating with the cylindrical surface of the workpiece. Each gauging head comprises a movable arm, carrying a feeler element for contacting the workpiece, and a position transducer.
The gauging heads, and in particular the movable arms, are mechanically protected by said legs of the support frame, by two bent legs integral with the first legs and by two metal plates fixed to the front and back sides of the frame. The first legs of the support frame protect the gauging heads mainly from impacts along the directions of mutual approach of the pairs of feeler elements and the metal plates protect the gauging heads mainly from impacts along the directions perpendicular to the directions of mutual approach of the feeler elements and to the longitudinal axis defined by the reference device.
This known gauge has a rather heavy, complex and expensive structure. In particular, the considerable weight is detrimental for the manual use of the gauge.
This known gauge is scarcely flexible, being adapted to check external diameters in a narrow measuring range.
A manual electronic snap gauge usable in different measuring ranges is also known. This snap gauge comprises a U-shaped support structure, to which there are fixed two adjustable elements or bearing pads, which perform the functions of a Vee reference, and--at the sides of the U--two "cartridge" heads, which are separately adjustable, too.
This snap gauge, too, is rather expensive and bulky. Moreover, the adjustment operations are rather long and complex and therefore require a skilled operator, especially as far as the adjustment of the two bearing elements is concerned.
Another known manual electronic snap gauge, for the rest similar to the preceding one, uses, instead of two bearing pads, a single adjustable pad having a plane bearing surface which arranges tangentially to the surface of the workpiece, along a direction parallel to the line passing through the feelers.
Therefore, the pad is not capable, by itself, of guaranteeing a symmetrical positioning of the snap gauge with respect to the workpiece in such a way that the two sides of the U-support are at equal distance from the longitudinal axis of the workpiece.
U.S. Pat. No. 4,348,814 to Possati et al discloses a manual plug gauge for checking diameters of holes, including an arm-set substantially obtained from a single member of bent spring-steel plate having two lightened sections defining relevant rotation axes and two measuring arms movable about said rotation axes. The member is coupled to a ring body to which also are coupled a handle and a nose-piece which protects the arm-set and provides centering of the gauge with respect to the hole to be checked.
It is evident that most of the structure of this known plug gauge cannot be used for constructing a snap gauge.